The present invention relates generally to devices for use in vascular treatments. More particularly, the present invention relates to devices used in vascular treatments that incorporate a magnetic resonance visibility enhancing structure, the devices being adapted for use in magnetic resonance imaging.
Vascular stents are known medical devices used in various vascular treatments of patients. Stents commonly include a tubular member that is moveable from a collapsed, low profile, delivery configuration to an expanded, deployed configuration. In the expanded configuration, an outer periphery of the stent frictionally engages an inner periphery of a lumen. The deployed stent then maintains the lumen such that it is substantially unoccluded and flow therethrough is substantially unrestricted. However, various stent designs substantially distort the surrounding of the stent during a Magnetic Resonance Imaging procedure.
Magnetic Resonance Imaging (MRI) is a non-invasive medical procedure that utilizes magnets and radio waves to produce a picture of the inside of a body. An MRI scanner is capable of producing pictures of the inside of a body without exposing the body to ionizing radiation (X-rays). In addition, MRI scans can see through bone and provide detailed pictures of soft body tissues.
A typical MRI scanner includes a magnet that is utilized to create a strong homogeneous magnetic field. A patient is placed into or proximate the magnet. The magnetic field causes a small majority of the atoms with a net magnetic moment, also referred to as spin, to align in the same direction as the magnetic field. When a radio wave is directed at the patient's body, atoms precessing in the magnetic field with a frequency equal to the radiowave are able to adapt the radiowave energy, which causes them to “tumble over” and align in the opposite direction of the magnetic field. The frequency at which atoms with a net spin precess in a magnetic field is also referred to as the Larmor frequency. The opposing alignment is at a higher energy level compared to the original orientation. Therefore, after removing the radiowave, atoms will return to the lower energetic state. As the atoms return to the lower energetic state, a radio signal is sent at the Lamor frequency. These return radio waves create signals (resonance signals) that are detected by the scanner at numerous angles around the patient's body. The signals are sent to a computer that processes the information and compiles an image or images. Typically, although not necessarily, the images are in the form of 2-dimensional “slice” images.
An ability to effectively view areas proximate a stent during an MRI procedure is desirable. In particular, viewing areas inside and proximate a tubular member of a stent may be desirable both during deployment and after deployment of the stent in a patient. However, various current stent designs prevent adequate imaging of the area surrounding the stent. Instead, the images are distorted and thus cannot be used.
The visibility of the inside of current stent designs during MRI procedures is blocked for two reasons. First of all, the permanent influence of the surrounding magnetic field by stents containing ferromagnetic materials prevents adequate imaging. A second reason that adequate imaging of the area inside the stent is blocked relates to induction currents (Eddy currents), induced in the closed cell metal stent structure due to the changes in the magnetic field generated by the MRI system during image sequencing. The result is that the MR visibility of the inside of the stent is shielded.
It is possible to build a stent out of polymer or other non-conducting materials such as ceramics. Building stents out of such non-conducting materials would avoid either of these MR artifacts. However, stents made from materials such as these would require larger strut dimensions to maintain adequate stent mechanical performance as compared to stents made of metals.
The present invention addresses at least one of these or other problems, and/or offers other advantages over the prior art.